docs: def _get_bandfilenames(self):
          """Get the instrument rsr filenames"""
          for band in self.bandnames:
              LOG.debug("Band = %s", str(band))
              self.filenames[band] = os.path.join(self.path,
                                                  self.options[self.platform_name + '-' +
                                                               self.instrument][band])
              LOG.debug(self.filenames[band])
              if not os.path.exists(self.filenames[band]):
                  LOG.warning("Couldn't find an existing file for this band: %s",
                              str(self.filenames[band]))